Radiation-emitting devices are generally known and used, for instance as radiation therapy devices for the treatment of patients. A radiation therapy device generally comprises a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located in the gantry for generating a high energy radiation beam for therapy. This high energy radiation beam can be an electron or photon (X-ray) beam. During treatment, this radiation beam is trained on one zone of a patient lying in the isocenter of the gantry rotation.
In this arrangement, radiation is generated by applying an electron beam to a target to generate x-rays. The electron beam is typically generated in a linear accelerator that is powered by a klystron based power supply having a power output in the 10 to 30 kW range. FIG. 1 is a block diagram of a medical linear accelerator showing major components and auxiliary systems. Power supply 10 provides D.C. power to modulator 12. Modulator 12 includes a pulse forming network and a switch tube known as hydrogen thyratron. A thyratron is a low pressure gas device with a thermionic cathode. Over time, the cathode depletes itself. Thus, a thyratron has an inherent wear out mechanism. The high voltage pulses from modulator 12 are flat-topped D.C. pulses of a few microseconds in duration. These pulses are delivered to magnetron or klystron 14 and simultaneously to electron gun 16. Pulsed microwaves produced in magnetron or klystron 14 are injected into accelerator tube 20 via waveguide system 22. At the proper instant, electrons, which are produced by electron gun 16, are also pulse injected into accelerator tube 20. High energy electrons emerge from accelerator tube 20 in the form of a beam of approximately 3 mm in diameter. These electrons can be fed to treatment head 24 as a straight beam or to treatment head 26 as a bent beam. If the electrons are sent to treatment head 26, the electrons are bent by, for example, bending magnet 28 through a suitable angle (e.g., 270 degrees) between accelerator tube 20 and the target.
Prior art power supplies for linear accelerators are large, heavy devices that significantly increase the cost and size of the medical treatment system. One typical prior art system utilizes a high voltage transformer/rectifier system to generate a 21 kV DC power source from a conventional three-phase 208 V power source. The high voltage DC source is then used to generate a 15 kV pulse that is converted to the required 150 kV pulse via a high voltage pulse transformer. The high voltage transformer/rectifier assembly typically weighs 500 lbs. and occupies 8 cubic feet. As a result, the power supply must be housed in a separate cabinet from the linear accelerator. In addition to increasing the floor space needed to house the accelerator system, this additional cabinet requires special power transmission lines to couple the klystron output to the linear accelerator which further increases the cost and complexity of the system. Finally, the sheer weight of the system increases the cost of shipping.
Broadly, it is the object of the present invention to provide an improved high voltage power system for powering klystrons and the like. It is a further object of the present invention to provide a high voltage power system that requires less space than prior art high voltage power systems. It is a still further object of the present invention to provide a high voltage power system that is significantly lighter than prior art power supply systems. These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.